Track planner: integrate existing tracks into route

Since Menion wrote he will work on the track planner in the near future, I would like to propose an idea looming in my mind for some time now: make it possible to integrate already existing tracks into the route.

As even the best routing data will never be as good as local knowledge and/or personal preference, it would be nice to be able to include pre-planned tracks into the route.

For example, I would like to plan a mountainbike route with nice singletrail-downhills in it.

Over the years, I've saved some nice singletrails / combinations of singletrails I know and like in my Locus track database. I would love to be able to combine these into a route, letting Brouter calculate the sections in between.

Currently, I have to force Brouter to follow my "approved" singletrail combinations by using via points every time I plan such a route, even though I have these sections readily available as tracks in my Locus database.

Maybe there could be a popup when tapping the starting (or ending) point of an existing track in track planner which allows to integrate this track into the route (similar to the POI popup to add a via point). The route planning could then continue from the ending point of the (now integrated) track.